Field of the Invention
The present invention relates to a method for determining whether a toxic gas sensor is functioning properly at any particular time. Surprisingly, no toxic gas is needed to perform the test.
Toxic gas sensors are widely used for sensing a build-up in the concentration of a toxic gas, for example, carbon monoxide, methane, hydrogen sulfide, and others, to protect the lives of persons who are exposed to the toxic gas. It is essential that the toxic gas sensor operate reliably, and to this end it is desirable to test the operation of the sensor from time to time.
At the completion of the manufacturing process, the sensor is calibrated by exposing it to an accurately controlled concentration of the toxic gas and noting the output reading of the sensor. At this point there is no doubt that the sensor is functioning properly and can be depended upon to save lives.
Thereafter, the sensor is transported, handled, and put into daily use where it is exposed to a number of environmental stresses. After a period of such use, the sensors may be found to have changed due to aging, due to chemical reactions with environmental elements such as moisture, particulates, smoke, various gases, insects, soot, and oil vapors, and due to chemical instabilities. In most instances, these environmental stresses affect the functioning and sensitivity of the sensors. If the sensor ceases to operate continuously, or if its sensitivity becomes sufficiently degraded, the sensor can no longer be relied on to protect the lives of those who are depending on it. Thus, it is seen to be highly desirable to provide a simple and easy method for testing the toxic gas sensors from time to time, to assure that they are continuing to operate properly.
Initially, one might consider the possibility of providing to the users of the sensors actual samples of the toxic gases for performing this periodic testing. However, upon further consideration this does not seem to be a good solution because frequently the users of the sensors are not familiar with proper techniques for handling the toxic gases, and they normally would not have appropriate apparatus for handling the toxic gases, so that there would be a large risk involved. Of course, some toxic gases are more deadly than others, but an element of risk still remains.
The present invention is directed to a method for testing the operation of a toxic gas sensor without using any toxic gas.